The present invention relates to a reflective display, a light guide plate and a method of manufacturing a light guide plate.
A typical reflective display is capable of displaying with low power consumption, and because of the property, the reflective display has been expected to be applied to a display device for an information terminal. However, in the reflective display having no light source, a displayed image cannot be viewed in a low light environment. Therefore, in recent years, a reflective display having a front light on a viewing side of a liquid crystal display panel has been proposed. For example, a wedge-shaped light guide plate comprising a top prismatic surface with a slanted portion and a planar portion which are alternately arranged and a bottom planar surface as front and back main surfaces is disposed on the viewing side of the reflective liquid crystal display panel, so that when light supplied from the light source (source light) is incident from a side surface, the source light is supplied all over the viewing side of the liquid crystal display panel, and then is reflected on a surface of a reflective plate disposed on the back surface of the liquid crystal display panel so as to be emitted to the viewing side. At this time, the amount of or the presence/absence of light emitted from the liquid crystal display panel is controlled in each pixel so as to display an image by emitting light from each pixel like a self light-emitting element. In other words, the above wedge-shaped light guide plate has both functions of a light reflector and a light transmitter.
In such a conventional wedge-shaped light guide plate, in order to sufficiently function as the light transmitter, a planar portion of the top prismatic surface is required to be substantially parallel to the bottom surface, because if the planar portion of the top prismatic surface forms a large angle with the bottom surface, light emitted from the liquid crystal display panel is refracted due to a prism effect between the bottom surface and the planar portion of the top prismatic surface, and the refracted light adversely affects image display performance as a liquid crystal display.
Moreover, in order to sufficiently function as the light reflector, the source light is guided into the light guide plate substantially in the surface direction and then is reflected at the slanted portion of the top prismatic surface so as to be entered into the liquid crystal panel almost perpendicularly. Therefore, it is desired that the slanted portion be angled at approximately 45 degrees.
However, when the planar portion and the slanted portion are alternately arranged, the thickness of the light guide plate is gradually reduced with increasing distance from the side surface where the source light is supplied, so the difference in thickness between the side surface where the source light is supplied and the other side surface is 2 to 3 mm or more, and thereby the sectional shape of the light guide plate is wedge-shaped. In such a wedge-shaped light guide plate, a wedge-shaped gap occurring between a surface of the liquid crystal display panel and the light guide plate causes parallax.
Therefore, the applicant of the invention developed a board-shaped light guide plate disclosed in Japanese Unexamined Patent Application Publication No. 2000-111900. In the board-shaped light guide plate, the top prismatic surface includes pseudo-planar portions gradually raised with increasing distance from the light source and slanted portions gradually descended with increasing distance from the light source which are repeatedly arranged, and the height of the apex of each prism is substantially uniform. Thereby, without taking the asperities of the prisms into account, the macroscopic outer shape of the light guide plate can be formed not into a wedge shape but into a board shape, and the light guide plate can sufficiently function as the light reflector and the light transmitter. Therefore, the source light can be effectively and evenly used on the surface of the liquid crystal display panel.
However, the inventors of the present invention confirmed by an experiment, etc. of displaying an image on the screen of the reflective liquid crystal display using the above board-shaped light guide plate that despite the use of the above board-shaped light guide plate, lower contrast of the image displayed on the screen of the reflective liquid crystal display might be viewed. Moreover, the inventors confirmed by various experiments and considerations that a phenomenon of such lower contrast of the displayed image occurred because stray light or the like in the board-shaped light guide plate was reflected on the planar surface of the light guide plate, and then was mixed with light involved in the original display which was reflected on the back surface of the liquid crystal display panel and emitted to outside from the viewing side. Further, it was confirmed that such light reflected on the planar surface of the board-shaped light guide plate included a large amount of light with a wavelength of approximately xcex=550 nm which was equivalent to a high visible light range of human visibility, so when such light was mixed with the light involved in the original display, further lower contrast of the image was viewed on the screen.
In view of the foregoing, it is a first object of the invention to provide a reflective liquid crystal display and a light guide plate capable of eliminating a decline in virtual contrast properties of a reflective liquid crystal display using a board-shaped light guide plate such as the one disclosed in Japanese Unexamined Patent Application Publication No. 2000-111900 so as to view an excellent image. Moreover, it is a second object of the invention to provide a method of easily and reliably manufacturing such a light guide plate.
A reflective display according to the invention comprises a reflective liquid crystal display panel including a reflective plate on a back side, and controlling transmission of light being incident from a viewing side and then being reflected on the reflective plate toward the viewing side in each pixel so as to display; a light guide plate including a prismatic surface with a plurality of prisms formed thereon and a planar surface as front and back main surfaces of the light guide plate, and a side surface where light from a light source is supplied, the plurality of prisms being formed with a different pitch from an alignment pitch of the each pixel, the prismatic surface having a pseudo-planar portion forming an angle ranging from approximately 0.5 degrees to approximately 3.5 degrees with the planar surface and being gradually raised with increasing distance from the side surface and a slanted portion forming an angle ranging from approximately 40 degrees to approximately 60 degrees with the planar surface so as to reflect the light supplied from the side surface toward the planar surface and being gradually descended with increasing distance from the side surface, and the light guide plate being disposed so that the planar surface faces the viewing side of the liquid crystal display panel; a linear polarizing plate and a xcex/4 plate disposed between the light guide plate and the liquid crystal display panel; and an antireflective film disposed on the planar surface of the light guide plate so as to inhibit light reflection on the planar surface.
Another reflective display according to the invention comprises a reflective liquid crystal display panel including a reflective plate on a back side, and controlling transmission of light being incident from a viewing side and then being reflected on the reflective plate toward the viewing side in each pixel so as to display; a light guide plate made of a synthetic resin including a prismatic surface with a plurality of prisms formed thereon and a planar surface as front and back main surfaces of the light guide plate, and a side surface where source light is supplied, the plurality of prisms being formed with a different pitch from an alignment pitch of the each pixel, the prismatic surface having a pseudo-planar portion forming an angle ranging from approximately 0.5 degrees to approximately 3.5 degrees with the planar surface and being gradually raised with increasing distance from the side surface and a slanted portion forming an angle ranging from approximately 40 degrees to approximately 60 degrees with the planar surface so as to reflect the light supplied from the side surface toward the planar surface and being gradually descended with increasing distance from the side surface, and the light guide plate being disposed so that the planar surface faces the viewing side of the liquid crystal display panel; a linear polarizing plate and a xcex/4 plate disposed between the light guide plate and the liquid crystal display panel; an antireflective film disposed on the planar surface of the light guide plate so as to inhibit light reflection on the planar surface; and an adhesive layer disposed between the antireflective film and the planar surface of the light guide plate to adhere the antireflective film to a surface of the light guide plate.
A light guide plate according to the invention is disposed on a viewing side of a reflective liquid crystal display panel including a reflective plate on a back side, and controlling transmission of light being incident from a viewing side and being reflected on the reflective plate toward the viewing side in each pixel so as to display, and the light guide includes a prismatic surface with a plurality of prisms formed thereon and a planar surface as front and back main surfaces of the light guide plate, and a side surface where light from a light source is supplied, the light guide plate being made of a synthetic resin, the plurality of prisms being formed with a different pitch from an alignment pitch of the each pixel, the prismatic surface having a pseudo-planar portion forming an angle ranging from approximately 0.5 degrees to approximately 3.5 degrees with the planar surface and being gradually raised with increasing distance from the side surface and a slanted portion forming an angle ranging from approximately 40 degrees to approximately 60 degrees with the planar surface so as to reflect the light supplied from the side surface toward the planar surface and being gradually descended with increasing distance from the side surface, the light guide plate comprises: an adhesive layer made of Si with a thickness ranging from 1 nm to 10 nm on the planar surface; and an antireflective film made of a laminate including a combination of a high refractive index film using at least one selected from a Nb2O5 film, a Ta2O5 film and a TiO2 film and a low refractive index film using at least one selected from the group consisting of a SiO2 film and a MgF2 film on a surface of the adhesive layer.
In a method of manufacturing a light guide plate according to the invention, the light guide plate is disposed on a viewing side of a reflective liquid crystal display panel including a reflective plate on a back side and controlling transmission of light being incident from a viewing side and being reflected on the reflective plate toward the viewing side in each pixel so as to display, and the method comprising the steps of: forming an adhesive layer made of Si with a thickness ranging from 1 nm to 10 nm on a planar surface of the light guide plate made of a synthetic resin through vaccum evaporation or sputtering, wherein the light guide plate includes a prismatic surface with a plurality of prisms formed thereon and the planar surface as front and back main surfaces of the light guide plate, and a side surface where light from a light source is supplied, the plurality of prisms are formed with a different pitch from an alignment pitch of the each pixel, the prismatic surface has a pseudo-planar portion forming an angle ranging from approximately 0.5 degrees to approximately 3.5 degrees with the planar surface and being gradually raised with increasing distance from the side surface and a slanted portion forming an angle ranging from approximately 40 degrees to approximately 60 degrees with the planar surface so as to reflect the light supplied from the side surface toward the planar surface and being gradually descended with increasing distance from the side surface; and forming an antireflective film made of a laminate including a combination of a high refractive index film using at least one selected from a Nb2O5 film, a Ta2O5 film and a TiO2 film and a low refractive index film using at least one selected from the group consisting of a SiO2 film and a MgF2 film on a surface of the adhesive layer so as to inhibit light reflection on the planar surface of the light guide plate.
In the reflective display according to the invention, the light guide plate includes a prismatic surface with a plurality of prisms formed thereon and a planar surface as front and back main surfaces thereof, and a side surface where light from a light source is supplied. The plurality of prisms are formed with a different pitch from an alignment pitch of each pixel. The prismatic surface has a pseudo-planar portion forming an angle ranging from approximately 0.5 degrees to approximately 3.5 degrees with the planar surface, and being gradually raised with increasing distance from the side surface and a slanted portion forming an angle ranging from approximately 40 degrees to approximately 60 degrees with the planar surface so as to reflect light supplied from the side surface toward the planar surface, and being gradually descended with increasing distance from the side surface. The reflective display, the light guide plate, or the method of manufacturing the light guide plate according to the invention comprises an antireflective film disposed on the planar surface of the light guide plate, which faces the viewing side of the liquid crystal display panel, so the antireflective film inhibits light reflection on the planar surface of the light guide plate.
The word xe2x80x9capproximatelyxe2x80x9d is added before the amounts of the angle which the pseudo-planar portion forms with the planar surface and the angle which the slanted portion forms with the planar surface in the above light guide plate, because even if the angle is set at 0.5 degrees or 40 degrees as a set value, an error of a few percents is often introduced during manufacturing. Therefore, in order to take account of such error, the word xe2x80x9capproximatelyxe2x80x9d is added.
Moreover, in another reflective display according to the invention, the light guide plate is specifically made of a synthetic resin, and another reflective display is equivalent the above reflective display further comprising an adhesive layer formed between the antireflective film and the planar surface of the light guide plate. The adhesive layer adheres the antireflective film to the light guide plate.
In the light guide plate according to the invention, an adhesive layer made of Si with a thickness ranging from 1 nm to 10 nm is formed on the planar surface of the light guide plate made of a transparent synthetic resin. Further, the antireflective film is made of a laminate including a combination of a high refractive index film using at least one selected from a Nb2O5 film, a Ta2O5 film and a TiO2 film and a low refractive index film using at least one selected from the group consisting of a SiO2 film and a MgF2 film. The antireflective film is firmly adhered to the planar surface of the light guide plate with the adhesive layer in between.
The method of manufacturing a light guide plate according to the invention comprises the steps of forming the adhesive layer made of Si with a thickness ranging from 1 nm to 10 nm on the planar surface of the light guide plate made of a synthetic resin through vaccum evaporation or sputtering, and forming an antireflective film made of a laminate including a combination of a high refractive index film using at least one selected from the group consisting of a Nb2O5 film, a Ta2O5 film and a TiO2 and a low refractive index film using at least one selected from the group consisting of a SiO2 film and a MgF2 film on the surface of the adhesive layer so as to inhibit light reflection on the planar surface of the light guide plate. As the adhesive layer is disposed between the planar surface of the light guide plate and the antireflective film, an interface of the planar surface of the light guide plate and an interface of the antireflective film are firmly adhered each other.
Other and further objects, features and advantages of the invention will appear more fully from the following description.